Nuclear Science User Facilities 92 dose rate: α' precipitation was hardly observed in high-dose-rate heavy- ion-irradiated Fe–Cr alloys, but was observed in proton-, electron-, or neutron-irradiated Fe–Cr alloys. The chromium content of Cr-rich precipitates found in several studies is way below phase-diagram predic- tion, indicating strong effects due to ballistic mixing. Figure 2 shows the α' precipitates found in neutron-irradi- ated Fe–9Cr at two different irradia- tion temperatures.The decreasing number density of α' precipitates with increasing irradiation temperature agrees with the phase diagram. However, the chromium content of these α' precipitates is also found to be considerably lower than the values predicted by the phase diagram. Microstructure characterization of HT9 andT91 HT9 (12Cr) andT91 (9Cr) are high Cr F/M steels of great interest for applications in advanced reactors. In this project the specimens were irradiated to a relatively low dose level and then characterized usingTEM and APT.The mechanical properties were measured by nanoindenta- tion.A variety of radiation-induced microstructural changes were observed, including dislocation loops, radiation-induced precipitation, and segregation.The irradiation doses and thermal conditions were estimated using simulation methods, and the conditions investigated in this project are shown in Figure 3. Figure. 3 Temperature and dose range of the irradiated HT9 and T91 specimens investigated. Figure 2. 20 at.% Cr isosurfaces showing the α' precipitates in neutron-irradiated Fe-10Cr samples.